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The Immune System and
Disease
Chapter 40
What is a disease?
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A disease is any change, other than an
injury, that disrupts the normal functions of
the body.
What causes disease?
Bacteria
 Viruses
 Protists
 Fungi
 Worms
 Carcinogens
 Genes/Mutations
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Pathogens
Pathogens are disease causing agents.
 Diseases caused by pathogens are
generally called “infectious diseases.”
 Carcinogens or genetic disorders which
cause disease are not pathogens.
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The Germ Theory of Disease
Robert Koch and Louis Pasteur
 Infectious diseases are caused by
microorganisms commonly called germs.
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Koch’s Postulates
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Rules used to identify the microorganism that
causes a disease:
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The pathogen should always be found in the body of
a sick organisms and should not be found in a healthy
one.
The pathogen must be isolated and grown in a
culture.
When the cultured (grown) pathogen is placed in a
new host, the host should get the same disease.
The injected pathogen should be taken from the
second host and should be found to be identical to
the first one.
Pathogens
Viruses
 Bacteria
 Protists
 Worms
 Fungi
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Viruses
Do not contain cells and are not classified
as living.
 Contain either DNA or RNA surrounded by
a protein coat.
 Inject DNA or RNA into the host cell and
begin to replicate its DNA or RNA, taking
over the functions of the host cell.
 Diseases: cold, influenza (flu), smallpox,
warts
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Small Pox
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Symptoms occur in 317 days.
Symptoms include:
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High fever
Backache
Malaise (weakness)
Vomiting
Rash
Bacteria
Single-celled organisms
 Cause disease either by breaking down
the tissues of the infected organism for
food or by releasing toxins that harm the
body.
 Few are harmful to humans.
 Examples: Streptococcus infections,
diphtheria, botulism, and anthrax.
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Diphtheria
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Swollen neck (bull neck)
Soar throat
High fever
Vomiting
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Skin lesion on the leg
Protists
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Disease causing protists are single-celled.
Usually transmitted (spread) by insects.
Examples:
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Malaria
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African Sleeping Sickness
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Caused by Plasmodium, a protist that is spread from person
to person by mosquitoes.
Caused by Trypanosoma, also spread by mosquitoes.
Amebic dysentery
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Caused by Entamoeba caused by contaminated water
supplies.
Worms
Flatworms and roundworms
 Usually found in tropical regions of the
world.
 Examples:
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Schistosoma: infect people working in rice
fields.
 Tapeworm
 Hookworm
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Fungi
Most fungi are harmless.
 Athletes foot (ringworm)

Caused by Tinea
 The same fungus can infect the scalp (Tinea
capitis) and other areas of the body.
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How are diseases spread?
Physical contact
 Contaminated food and water
 Infected animals
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Physical Contact
Touch
 Body fluids
 Sneezing
 Coughing
 Sex
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Contaminated Food and Water
Food poisoning (spoiled food).
 Uncooked meat.
 Poor sanitation and untreated sewage
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Infected Animals
Vectors: animals that carry pathogens
from person to person (mosquitoes).
 Examples: Malaria, Lyme disease, West
Nile Virus, and rabies.
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Antibiotics
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Antibiotics are compounds that kill bacteria
without harming the cells of the human or
animal hosts.
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Penicillin (produced by mold): discovered by
Alexander Fleming
Antibiotics have no effects on viruses.
Immune System
The function of the immune system is to
fight infection through the production of
cells that inactivate foreign substances or
cells.
 This process is called immunity.
 The immune system includes two general
categories of defense:
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nonspecific defenses
 specific defenses
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Nonspecific Defenses
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Nonspecific defenses include physical and chemical
barriers.
First Line of Defense: skin
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Very few pathogens can penetrate the layers of dead cells at the
skin’s surface.
The importance of the skin as a barrier against infection
becomes obvious as soon as it is broken.
Secretions of the body including mucus, saliva, and tears
contain lysozyme, an enzyme that breaks down the cell
walls of many bacteria.
Pathogens that enter the body through the nose or throat
can be trapped by mucus and cilia (tiny hairs), which
help push pathogens away from your lungs.
Second Line of Defense
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If pathogens do enter your body, they multiply
quickly, releasing toxins into your tissues.
Inflammatory response: blood vessels near the
wound expand and white blood cells move from
the vessels to enter the infected tissues. The
infected tissue may become swollen and painful.
Fever: elevated body temperature, kills
pathogens, which can usually only survive within
a narrow temperature range. Elevated
temperature also increases the heart rate so that
WBC’s get to the site of infection faster.
Specific Defenses
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If a pathogen is able to get past the non-specific
defenses, the immune system response with specific
defenses that attack the particular disease-causing
agents: immune response.
A substance that triggers this response is called an
antigen.
The cells of the immune system which recognize specific
antigens are either B lymphocytes (B cells) or T
lymphocytes (T cells).
Humoral immunity: B cells provide immunity against
antigens and pathogens in body fluids.
Cell-mediated immunity: T cells provide defense against
abnormal cells and pathogens inside living cells.
Humoral Immunity
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B cells grow and divide rapidly, produce large numbers
of plasma cells and memory B cells.
Plasma cell release antibodies, proteins that recognize
and bind to antigens.
The antibodies are carried in the bloodstream to attack
the pathogen that is causing the infection.
As the antibodies overcome the infection, the plasma
cells die out and stop producing antibodies.
Once the body has been exposed to a pathogen, millions
of memory B cells remain capable of producing
antibodies specific to that pathogen, reducing the chance
that the disease could develop a second time.
Cell-Meditated Immunity
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The body’s primary defense against its own cells
when they have become cancerous or infected
by viruses.
T cells divide and differentiate into killer T cells,
helper T cells, suppressor T cells, and memory T
cells.
Killer T cells: track down and destroy the
pathogen.
Helper T cells: produce memory T cells, act
similar to memory B cells.
Suppressor T cells: release substances that shut
down the killer T cells.
Vaccinations
A vaccination is an injection of a
weakened or mild form of a pathogen to
produce immunity.
 Edward Jenner produced
the first vaccination, using a form
of smallpox which came from a cow
(cowpox).
 Active immunity: the type of immunity
produced by the body’s reaction to a
vaccine or natural exposure.
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Immune System Disorders
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3 types of immune system disorders:
Allergies
 Autoimmune disease
 Immunodeficiency diseases
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Allergies
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Allergies are a common overreaction of the immune
system to antigens.
Common allergies include: pollen, dust, mold, and bee
stings.
When allergy causing antigens enter the body, they
attach themselves to mast cells.
Mast cells are specialized immune system cells that
initiate the inflammatory response.
The activated mast cells release chemicals known as
histamines, which increase the flow of blood and fluids to
the surrounding area.
They also increase mucus production (causing sneezing,
watery eyes, runny nose, coughing, etc).
If you have allergies you have probably taken
antihistamines (allegra, zyrtec, etc)
Autoimmune Disease
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When the immune system makes a mistake and
attacks the body’s own cells, it produces an
autoimmune disease.
Examples:
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Type I diabetes: antibodies attack insulin-producing
cells of the pancreas.
Rheumatoid arthritis: antibodies attack connective
tissues around the joints.
Myasthenia gravis: antibodies attack neuromuscular
junctions.
Multiple Schlerosis (MS): antibodies destroy the
functions of the neurons in the brain and spinal cord.
Immunodeficiency Diseases
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AIDS (acquired immunodeficiency): results from a viral
infection (HIV) that destroys helper T cells.
Discovered when patients were dieing due to what were
normally non-serious infections.
They were dieing as a result of a previous infection
(HIV).
As the number of helper T cells declines the normal
immune response breaks down.
The progression of HIV infection can be monitored by
counting the number of helper T cells.
The fewer the helper T cells the more advanced the
disease.
Transmission of HIV (human
immunodeficiency virus)
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There are 4 main ways to transmit HIV:
 Through any form of sexual intercourse with an
infected person.
 Through shared needles or syringes that are
contaminated with the blood of an infected
person.
 Through contact with blood or blood products of
an infected person.
 From an infected mother to child, either during
pregnancy, during birth, or during breast-feeding.
Is there a cure?
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There is no cure or vaccine at present
there is only a “cocktail” of expense
medicines and vitamins allowing people to
live with HIV instead of dieing from it.
How can you stay healthy?
Eat right.
 Exercise and rest.
 Abstain from harmful activities.
 Get regular checkups.
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